Deformable lumen support devices and methods of use

ABSTRACT

Lumen support devices and methods of their use are provided. A lumen support includes one or more plastically deformable cells having two stable configurations with no stable configurations between the two stable configurations. The lumen support device may be plastically deformed to other stable configurations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit under 35 U.S.C. §119(e) ofthe provisional application 60/853,245, filed Oct. 21, 2006 which ishereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments described herein relate to lumen supports having plasticallydeformable structures.

Description of Related Technology

Vascular prostheses, commonly referred to as stents, are now widely usedin interventional procedures for treating lesions of the coronaryarteries and other vessels. Such devices generally have a tubular shapeand are deployed in a vessel, and are intended to restore and maintainthe patency of a segment of a vessel. Previously-known vascularprostheses are generally either self-expanding or balloon expandable,and may vary in size, shape or other characteristics depending onwhether the use is for the cardiac vasculature, carotid arteries, renalarteries, superficial femoral arteries, or other vessels.

Self-expanding and balloon expandable stents often have elasticitiesassociated with a relatively large amount of recoil. As such, the stentmay be prone to recoil inward after being expanded to its maximum outerdiameter. If this recoil is significant, the stent may not remainstationary relative to the passageway, instead migrating to a point oflesser desirability. As a result, serious or fatal injury to the patientmay occur.

Another aspect of stents is the size to which they may be compactedthrough crimping. Stents may be crimped onto a catheter for delivery toa lesion location within a lumen. One manner of crimping involves theapplication of a force directed in a radially inward direction to forcethe stent into a compact profile. However, the stent's diameter may tendto recoil to a diameter greater than its minimum diameter. This recoiltypically increases as the material's elasticity increases. Onedisadvantage of this phenomenon is that, with increased recoil aftercrimping, the stent's delivery profile is increased, thereby limitingthe stent's applicability to small vessels that would otherwise beaccessible by a stent with a smaller delivery profile. Anotherdisadvantage is that a stent that is not tightly coupled to the deliverycatheter may become dislodged at an undesirable location duringdelivery.

Different material choices for stents or other medical devices offerdifferent advantages and disadvantages. For example, some highly elasticmaterials have increased strength and/or increased radiopacity whencompared to other materials with a lower elasticity, yet suffer fromgreater recoil than materials with a lesser elasticity. A balance isdesired in which beneficial features of such stent materials may beenjoyed while reducing disadvantages such as recoil.

SUMMARY OF THE INVENTION

In view of the foregoing drawbacks of previously-know vascularprostheses and other similar medical devices, one aspect of certainembodiments described herein is to provide a lumen support having one ormore unit cells. In particular embodiments, the one or more unit cellsare capable of assuming multiple stable configurations. In one aspect ofcertain embodiments, the lumen support having the one or moremultistable unit cells comprises beneficial features of elasticmaterials. Another aspect of certain embodiments is to provide a lumensupport having one or more multistable cells that do not significantlyincrease in diameter due to recoil following crimping. Yet anotherobject of certain embodiments is to provide a lumen support that doesnot significantly decrease in diameter due to recoil followingexpansion.

These and other advantages are achieved by providing a supportivestructure having a body comprising a plurality of cells capable of lowrecoil due to some reversal of elastic strain when crimped. The cellsfurther may undergo plastic deformation as the medical device isdeployed into an expanded configuration, and the asymmetrical shape ofthe cells reduces the degree of recoil in comparison to known stentdesigns. In certain embodiments, such a supportive structure iswell-adapted to be formed of certain elastic materials such as cobaltalloys and stainless steel, thereby being capable of enjoying theadvantages of strength and/or radiopacity, with a reduction in effectssuch as recoil.

In one embodiment, a lumen support is configured to be expanded andcontracted to a plurality of stable positions. In some embodiments, thesupport includes a plurality of cells. In some embodiments, each of theplurality of cells is defined by at least a first segment and a secondsegment. In some embodiments, the cell includes a first stable collapsedconfiguration, a second stable collapsed configuration, a first stableexpanded configuration, and a second stable expanded configuration. Incertain embodiments, the first segment, is made of a material having anelastic range of between about 0.15 to about 1% and an elongation ofabove 30% and an ultimate tensile strength greater than 500 MPa. Asdiscussed further herein, the strut made of this material exhibitsreduced recoil to an applied force. In some embodiments, the secondsegment is less flexible than the first segment. In certain embodiments,the first segment may transition from a first stable contracted positionto a first stable expanded position relative to said second segment.This transition causes the cell to transition from the first stablecollapsed configuration to the first stable expanded configuration. Insome embodiments, the first segment is configured to plastically deformto a second stable contracted position creating an area for each cellless than the area created when said first segment is at said firststable contracted position. In some embodiments, the first segment isconfigured to plastically deform to a second stable expanded positioncreating an area for each cell greater than the area created when saidfirst segment is at said first stable expanded position. In someembodiments, the first segment is configured to transition betweencontracted and expanded positions through an inversion point in whichforce is reduced in order to complete the transition. In someembodiments, the first segment has an elastic range of between about 0.3to about 0.8%. In some embodiments, the first segment substantiallyconforms to the shape of the second segment in the first stablecollapsed configuration. In some embodiments, the second segmentcomprises a plastically deformable segment made of the material of thefirst segment.

In another embodiment, a lumen support includes a plastically deformablestructure made of a material having an elastic range between about 0.15to about 1% and an elongation of above 30% and an ultimate tensilestrength greater than 500 MPa. Such structure is capable of assuming anoriginal collapsed configuration or a plastically deformed collapsedconfiguration and an original expanded configuration or a plasticallydeformed expanded configuration, wherein no stable configurations existbetween the original collapsed configurations or the original expandedconfiguration. In certain embodiments, the structure is defined in partby a first segment and a second segment, the first segment being moreflexible than the second segment. In certain embodiments, the firstsegment is capable of transitioning between a contracted position and anexpanded position, relative to the second segment, wherein the firstsegment passes a transition point between the contracted position andthe expanded position that allows force to be decreased during thetransition.

In another embodiment, a method of crimping a lumen support on adelivery device is described. Such method may include delivering a lumensupport onto a delivery device. Lumen supports are further discussedherein and can be used with any embodiment or feature of any lumensupport described herein. The method may further include applying aradially inward force to the lumen support, and deforming one or moreunit cells of the lumen support to a plastically deformed collapsedconfiguration. In certain embodiments, the method may includetransitioning the lumen support to a stable collapsed configuration froma stable expanded configuration by application of a force through aninversion point of decreased force. In one embodiment, the lumen supporthas a smaller diameter in the plastically deformed collapsedconfiguration than in the stable collapsed configuration. In oneembodiment, the lumen support includes a first segment and a secondsegment, the first segment being more pliable than the second segment.In certain embodiments, the lumen support includes a material having anelastic range between about 0.15 to about 1% and an elongation of above30% and an ultimate tensile strength greater than 500 MPa.

In another embodiment, a lumen support includes a plurality of unitcells arranged in a first column and a second column, the first andsecond columns having a tubular shape and being interconnected by atleast one flexible connector. In some embodiments, each unit cell in thefirst column of unit cells is coupled by first flexible articulations.In some embodiments, each unit cell in the second column of unit cellsis coupled by second flexible articulations. In some embodiments, atleast some of the unit cells of the plurality of unit cells are capableof transitioning between a stable expanded configuration and a stablecollapsed configuration by application of a force through an inversionpoint of decreased force. In some embodiments, the first flexiblearticulations and the flexible connector are configured to allow one ormore unit cells of the first column to conform to a lumen. In certainembodiments, the plurality of unit cells is made of a material having anelastic range between about 0.15 to about 1% and an elongation of above30% and an ultimate tensile strength greater than 500 MPa. In someembodiments, the material is a cobalt alloy or is stainless steel.

In another embodiment, a balloon catheter includes a balloon and a lumensupport device in a crimped configuration coupled to the balloon. In oneembodiment, the device includes one or more unit cells capable oftransitioning from a stable collapsed configuration to a stable expandedconfiguration by application of a force through an inversion point ofdecreased force. In some embodiments, the one or more unit cells arecapable of plastically deforming to an expanded plastically deformedconfiguration. In some embodiments, the lumen support device includes amaterial having an elastic range between about 0.15 to about 1% and anelongation of above 30% and an ultimate tensile strength greater than500 MPa. In some embodiments, the material is a cobalt alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention willbe apparent upon consideration of the following detailed description,taken in conjunction with the accompanying drawings, in which likereference characters refer to like parts throughout, and in which:

FIG. 1 is a supportive structure in a stable expanded configuration inaccordance with one embodiment;

FIG. 2 is a supportive structure in a stable collapsed configuration inaccordance with one embodiment;

FIG. 3A is graph comparing the crimp force to the reduction in diameterbetween a stent constructed in accordance with one embodiment andanother stent of a known design;

FIG. 3B is a drawing of various unit cell configurations as correlatedto points on the graph of FIG. 3A

FIG. 3C is a graph which shows crimping of unit cells shown in FIG. 3Bas well as expansion through an inversion point to a plasticallydeformed configuration;

FIG. 4 is a section of a support structure in a first stable expandedconfiguration that is displayed in a flattened profile in accordancewith one embodiment;

FIG. 5 is a section of a supportive structure in a first stablecollapsed configuration that is displayed in a flattened profile inaccordance with one embodiment;

FIG. 6A is a section of a supportive structure in a plastically deformedexpanded configuration that is displayed in a flattened profile inaccordance with one embodiment;

FIG. 6B is a section of a supportive structure is a plastically deformedcollapsed configuration that is displayed in a flattened profile inaccordance with one embodiment;

FIG. 7 is a section of a supportive structure that is displayed in aflattened profile in accordance with one embodiment;

FIG. 8 is a section of a supportive structure that is displayed in aflattened profile in accordance with one embodiment;

FIG. 9 is a section of a supportive structure that is displayed in aflattened profile in accordance with one embodiment;

FIGS. 10A-10E depict two cells from the embodiment of FIG. 7 in aflattened profile and in variety of configuration in accordance with oneembodiment;

FIGS. 11A-11E depict a column of cells from the embodiment of FIG. 7 ina variety of configurations in accordance with one embodiment.

FIGS. 12A-12B depict one embodiment of a supportive structure accordingto one embodiment in an expanded and a collapsed configuration;

FIG. 13 is a schematic drawing of a process of crimping a unit cell froma stable expanded configuration through a stable collapsed configurationto a plastically deformed collapsed configuration;

FIGS. 14A-14B are schematic drawings comparing a conventional crimpingprocess for a stent to the crimping process for the improved stent;

FIG. 15 is a schematic drawing comparing recoil of plastically andelastically expanded stents;

FIG. 16 is a drawing of one embodiment of two cells of a supportivestructure having certain features;

FIG. 17 is a drawing of a crimped stent;

FIGS. 18A-18B are drawings of open cell embodiments having expanded andcollapsed configurations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Certain embodiments include a supportive structure that comprises one ormore cells having a stable collapsed configuration and a stable expandedconfiguration. In particular embodiments, the supportive structure maybe at least a part of a medical device. Unless otherwise indicated, theterm “medical device” is a broad term and is used in its ordinary senseand includes, without limitation, wherein the context permits, stents,stent delivery devices, valves, multi-stable valves, occlusion devices,expanders, clips, loops, rings, and other devices including cells,whether open or closed. In particular embodiments, the supportivestructure comprises one or more cells in a tubular form. In certainembodiments, a tubular device is described in terms of “diameter” of aportion of the tubular structure. While tubular embodiments havingcircular cross-sections (e.g., of constant diameter along its length)are sometimes preferred, other embodiments are not limited to thatgeometry. As such devices within the scope of the present invention mayalso include tapered portions, conical flares, curved portions,branches, or have other similar geometrical features known in the art.

An example of such a supportive structure is shown in U.S. Pat. No.6,488,702 (also referred to herein as “the Besselink patent”), which ishereby incorporated by reference in its entirety. Notably, the Besselinkpatent describes bistable and multistable devices that have two or morestable configurations. In particular, the Besselink patent describes adevice having one or more unit cells having a stable collapsedconfiguration and a stable expanded configuration. As a cell transitionsfrom the stable collapsed configuration to the stable expandedconfiguration, the cell transitions through a transition point at whichthe force required to complete the transition is decreased.

In contrast to the Besselink patent, a supportive structure of certainembodiments described herein may be deformably collapsed or expanded toa continuous range of discrete diameters less than or greater than thediameter of the stable collapsed configuration or the stable expandedconfiguration of the device. As such, devices described herein mayinclude one or more unit cells that have stable collapsed and expandedconfigurations. Such configurations elastically resist minordeformations. As noted, the cell may transition from a stable collapsedconfiguration to a stable expanded configuration through a transitionpoint of decreased force. The transition point allows the stent toassume the opposite configuration without additional application offorce. Such expansion or contraction may be defined as isothermal incertain embodiments. Once in a stable configuration, whether collapsedor expanded, the cell may then be plastically deformed to an expanded orreduced area. Following such plastic deformation, some degree of recoilresults in the unit cell assuming a plastically deformed configuration.

As used herein, the phrase “predetermined stable state” or“predetermined stable configuration” describes a configuration in whichone or more cells of the device are in a known configuration thatelastically resists change in a manner such that the cell returns to theknown configuration following minor deformations. As an example, abistable cell of the Besselink patent may have two predetermined stableconfigurations, an open configuration and a closed configuration. Suchpredetermined configurations may be determined upon manufacture of thedevice. A cell may “snap” from one configuration to the other inresponse to a threshold force that displaces a portion of the cellbeyond an intermediate or transition point. These configurations are notonly stable, but are predetermined based on the design of the cell. Incertain embodiments, a predetermined stable configuration may alsoinclude a plastically deformed configuration after recoil. As such,where context permits, predetermined may also be used to describe aplastically deformed configuration.

In certain embodiments, the plastically deformed state of one or morecells may be described in terms of increased or decreased area of theunit cell. In some embodiments, the one or more unit cells may beplastically deformed from the original stable collapsed configurationhaving a first area to a plastically deformed stable collapsedconfiguration having a second area less than the first area. Likewise,the one or more unit cells may be plastically deformed from the originalstable expanded configuration having a first area to a plasticallydeformed stable expanded configuration having a second area greater thanthe first area.

Once plastically deformed in one configuration, the one or more unitcells assume the plastically deformed configuration as one of the twostable configurations of the unit cell. For example, a cell that hasbeen plastically deformed from the original stable expandedconfiguration to a plastically deformed stable expanded configurationwill assume the plastically deformed stable configuration of the cell.In some embodiments, such a cell may be capable of transitioning back toa collapsed configuration by applying requisite force to the cell.Likewise, according to some embodiments, the one or more unit cells maybe plastically deformed to a plastically deformed collapsed position bycrimping, and then expanded to the predetermined stable expandedconfiguration or beyond into a range of plastic deformation. In certainembodiments, a plastically deformed cell may be further plasticallydeformed as desired and where the structural integrity of the cellpermits.

In certain embodiments, the medical device having the one or more cellsis made of an elastic material having certain mechanical and physicalproperties. Applicants have unexpectedly discovered that certainmaterials may resist recoil upon being compressed or collapsed orexpanded to a plastically deformed state when used in combination withthe geometry and structure of unit cells described herein. In particularembodiments, optimal materials may include materials having certainultimate tensile strengths, elongation percentages, and/or elasticranges. In certain embodiments, one material used in forming the medicaldevice has an ultimate tensile strength of greater than about 500 MPa,an elongation of greater than about 30%, and an elastic range betweenabout 0.15 and about 1%. In certain embodiments, one material used informing the medical device has an ultimate tensile strength betweenabout 500 MPa and about 2000 MPa, an elongation of greater than about25%, and an elastic range between about 0.15% and about 0.8%. Otherpotential ranges for materials are further described below.

In some embodiments, the material may have an elastic range that isgreater than or equal to about 0.20%. In certain embodiments, the one ormore cells are made of an elastic material having an elastic range ofbetween about 0.15% and about 0.8%. In certain embodiments, the one ormore cells are made of an elastic material having an elastic range ofbetween about 0.2% and about 0.7%. In certain embodiments, the one ormore cells are made of an elastic material having an elastic range ofbetween about 0.3% and about 0.9%. In certain embodiments, the one ormore cells are made of an elastic material having an elastic range ofbetween about 0.2% and about 0.6%.

In some embodiments, the material may have an ultimate tensile strengththat is greater than or equal to about 500 MPa. In certain embodiments,the one or more cells are made of a material having an ultimate tensilestrength of between about 450 MPa and about 2000 MPa. In certainembodiments, the one or more cells are made of a material having anultimate tensile strength of between about 600 MPa and about 1500 MPa.In certain embodiments, the one or more cells are made of a materialhaving an ultimate tensile strength of between about 550 MPa and about1200 MPa. In certain embodiments, the one or more cells are made of amaterial having an ultimate tensile strength between about 650 MPa andabout 1000 MPa.

In some embodiments, the material may have an elongation that is greaterthan or equal to about 30%. In certain embodiments, the one or morecells are made of a material having an elongation of between about 25and about 75%. In certain embodiments, the one or more cells are made ofa material having an elongation of between about 30% and about 60%. Incertain embodiments, the one or more cells are made of a material havingan elongation of between about 35% and about 55%.

It will be appreciated that examples of suitable materials fallingwithin these ranges include cobalt alloys. In some embodiments, cobaltnickel chromium alloys may be used. In some embodiments, cobalt chromiumnickel alloys may be used. Nonlimiting examples of such cobalt alloysinclude, but are not limited to L-605 or MP35N. In certain embodiments,cobalt-chromium alloy is a suitable material to use in forming stents orother medical devices, as it has greater radiopacity than othermaterials commonly used to form stents. As such, a smaller amount ofcobalt-chromium alloys may be used compared to other known materials.While some embodiments include unit cells made in part ofcobalt-chromium alloy, embodiments may also be practiced with materialshaving similar mechanical properties as described herein. In onenonlimiting embodiments, a stainless steel alloy may be used. Inparticular, a stainless steel alloy may include 316 SS. Other suitablematerials may include polymeric materials or bioabsorbable materials.Physical and mechanical properties of the above-mentioned suitablematerials are found in Table 1, copied from Poncin, P. et al., StentTubing: Understanding the Desired Attributes, Materials & Processes forMedical Devices Conference, September 2003, which is hereby incorporatedby reference in its entirety.

TABLE 1 Physical and mechanical properties of selected materials.ULTIMATE ELASTIC TENSILE 0.2% YIELD UTS- ELASTIC DENSITY MODULUSSTRENGTH STRENGTH YIELD ELONG. RANGE gr/cm³ G Pa MPa MPa MPa % %STAINLESS STEELS Fe—18Cr—14Ni—2.5Mo 7.95 193 670 340 330 48 0.17“316LVM” ASTM F138 Fe—21Cr—10Ni—3.5Mn—2.5Mo 7.90 195 740 430 310 35 0.22ASTM F 1586 Fe—22Cr—13Ni—5Mn 7.88 193 827 448 379 45 0.23 ASTM F 1314Fe—23Mn—21Cr—1Mo—1N 7.63 190 931 607 324 49 0.32 Nickel free SS COBALTALLOYS Co—20Cr—15W—10Ni 9.10 243 820-1200 380-780 420-600 35-550.16-0.32 “L605” ASTM F90 Co—20Cr—35Ni—10Mo 8.43 233 930 414 516 45 0.18“MP35N” ASTM F 562 Co—20Cr—16Ni—16Fe—7Mo 8.30 221 950 450 500 45 0.20“Phynox” ASTM F 1058 TITANIUM ALLOYS CP Titanium 4.50 107 300 200 100 300.19 ASTM F 67, Grade 1 Ti—6Al—4V 4.43 105 860 795 65 10 0.72 Alpha/betaASTM F 136 Ti—6Al—7Nb 4.74 106 1000 900 100 12 0.85 Alpha/beta ASTMF1295 Ti—15Mo 4.95 83 793 655 168 22 0.79 Beta grade ASTM F2066REFRACTORY Tantalum 16.60 185 207 138 69 25 0.06 Niobium 8.57 103 195105 90 25 0.10 Tungsten 19.3 411 3126 3000 126 3 0.73 Molybdenum 10.2324 1540 1386 154 15 0.43 PRECIOUS Pt—10Ir 21.55 150 340 200 140 25 0.13NITINOL Martensitic 6.45 40 1200 200-300  900-1000 25 1.9 Cold worked40% 6.45 40 1450 NS NS 12 4-6 Superelastic 6.45 90 1400 NS NS 14 6-8MAGNESIUM Mg3Al—1Z 1.8 45 255 162 93 10-25 0.36

In one embodiment, a support structure is provided having one or morecells defined by at least two sections, wherein one section is morepliable than another section. Each unit cell may be formed of at leasttwo distinct, mechanically connected sections with different mechanicalbehaviors. One section acts as a relatively rigid support for the moreflexible section. In certain configurations, the more flexible sectionis responsible for most, if not all, of the expansion of the stent. Insome embodiments, a cell includes two interconnected sections of unequaldimensions. In one embodiment, a cell may include two struts havingunequal thicknesses, widths, and/or cross sections. For example, a firststrut may have a thickness less than the thickness of a second strut.

In some embodiments, a first strut of the cell is configured to be moreflexible than a second strut of the cell. In certain embodiments, thefirst and second struts are each concave in shape in a collapsedconfiguration. In certain embodiments, the first strut has substantiallythe same shape as the second strut in a collapsed configuration. Themore flexible or pliable first strut may be transitioned from a firststable collapsed position having a first distance from the second strutto a first stable expanded position having a second distance from thesecond strut, the second distance being greater than the first distance.

Based on the geometry of the struts, this transition of the first strutfrom the first stable collapsed position to a first stable expandedposition requires the application of some amount of force until thefirst strut passes through a transition point, after which time thefirst strut may continue expanding to the stable expanded configurationposition without any additional force being applied. Similarly, thefirst strut may move from the stable expanded configuration position tothe stable collapsed position, requiring an amount of force required toreach a transition point, after which time the first strut continues tomove to the collapsed configuration position without any additionalforce being applied.

Additional force may be applied to the structure in either the stablecollapsed configuration or the stable expanded configuration to achieveadditional and useful expanded and/or collapsed configurations. Incertain embodiments, a unit cell in a stable collapsed configuration maybe deformed to have a second stable collapsed configuration whereby thearea of the unit cell is decreased. In particular embodiments, thestructure is plastically deformed by crimping. Plastically deforming theunit cell to a plastically deformed collapsed configuration can occurwith sufficient force to impart a desired reduced area of the unit cell.Such plastic deformation causes the medical device comprising the one ormore unit cells to reach and substantially maintain a compressedgeometry. In certain embodiments, the compressed geometry is suitablefor delivery of the medical device within a body lumen. Likewise, one ormore cells of the medical device may be plastically deformed beyond theoriginal stable expanded configuration to a plastically deformed stableexpanded configuration by the application of an outward force. Suchplastic deformation causes the medical device comprising the one or moreunit cells to reach and substantially maintain an expanded geometry.

In certain embodiments, plastic deformation of the first, more flexiblestrut is used to achieve plastically deformed stable configurations. Forexample, an amount of force sufficient to plastically deform the firststrut may be applied when the first strut is in a collapsed position.Such force is typically applied at least in part in a direction towardthe second less flexible strut. The plastically deformed first stmtattains a second collapsed or contracted position having a distancecloser to the second strut. In some embodiment, the second, lessflexible strut may also experience plastic deformation or geometricalvariance with the deformation of the first strut.

Once plastic deformation has occurred to a plastically deformedcollapsed configuration, the cell does not return to predeterminedstable collapsed configuration. Likewise, once plastic deformation hasoccurred to a plastically deformed expanded configuration, the cell doesnot return to predetermined stable expanded configuration. Instead, thecell substantially maintains its collapsed or expanded configuration towhich it was plastically deformed. It will be appreciated that the sizeand shape of the cell may be gradually decreased or increased byadditional plastically deforming force, thereby allowing the stent to becollapsed or expanded through a continuum of diameters, perimeters,cross-sectional areas and/or sizes.

Certain embodiments include the unit cells described herein. In oneembodiment, a one unit cell device may be used. For example, one unitcell lumen support may be used. In certain embodiments, unit cells ofcertain embodiments include one or more unit cells in a column, suchcolumn being arranged in a tubular structure. In certain embodiments,one or more columns may be connected together as further describedherein. In certain embodiments, rings of the multistable unit cellshaving an inversion point between expanded and collapsed configurations,may be used together with convention unit cells that do not have theinversion geometry discussed herein. For example, one ring of enhancedunit cells (i.e., having an inversion point geometry) may be adjacent toa ring of conventional unit cells that do not posses such inversionpoint geometry.

Embodiments will now be described with reference to the drawingsprovided. Although embodiments will be discussed in connection withcertain medical devices shown in the drawings, it is understood thatsuch discussion is to facilitate an understanding of the preferredembodiments only, and is not intended to limit the scope of the presentapplication to the embodiments shown in the figures.

As presently contemplated, one embodiment of a medical device having oneor more cells is a stent. Alternatively, embodiments of the medicaldevices described herein could take the form of a multistable valve, anexpander, a clip, a loop, a ring, or other like medical devices and/orlumen supports which use expandable cells. For the sake of simplicity,embodiments relating to stents are described below.

Referring now to FIGS. 1 and 2, an embodiment of a supportive structurein the form of stent 10 is shown. Stent 10 includes a plurality of cellshaving at least bistable configurations described in greater detail inthe Besselink patent. Stent 10 comprises a number of thick struts 12interconnected to thin struts 14 by connector members 16. Thick struts12 typically have different dimensions than thin struts 14. For example,thick struts 12 may have a greater thickness, width, or cross-sectionthan thin strut 14. In a preferred embodiment in which the thicknessesof struts 12 and 14 are different, thick struts 12 are between about 1%to about 200% thicker than thin struts 14, although it will beappreciated that the strut thicknesses may be equal or may be differentby some amount outside this range.

Stent 10 may comprise one or more materials. In particular embodiments,stent 10 comprises a material having a certain elastic range,elongation, and ultimate tensile strength as noted above. In someembodiments, stent 10 is at least partially formed of such a material.In some embodiments, stent 10 is fully formed of such a material. Insome embodiments, thin struts 14 are partially or fully made of acobalt-chromium alloy. In certain embodiments, thick struts 12 arepartially or fully made of a cobalt-chromium alloy. Stent 10 may beformed of a uniform material or may be a combination of one or morematerials. For example, some embodiments may include thin struts 14formed of a first material and thick struts 12 formed of a secondmaterial.

The construction of stent 10 includes a series of elements with anarrangement of unit cells that enable stable expanded and stablecollapsed configurations. There are several ways to manufacture a stentbased upon this principle. In certain embodiments, an arrangement ofwire or strips may be welded together at specific places. The particularpattern or arrangement can also be made in a flat plate and then welded,brazed or crimped to a more or less cylindrical shape or a cylindricalmid section with two conical ends with larger diameters. Anotherpossibility is metal deposition in the desired pattern onto a substrateor the use of sintering of prealloyed powder. A further method is makingthe stent from a tubular shaped starting material, such as a hollow tubeof cobalt-chromium alloy, with a pattern of slits or slots made in thewall by means of etching, grinding, cutting (e.g., with a laser, water,etc.), spark erosion or any other suitable method. In some embodiments,unit cells are manufactured in a collapsed configuration such that theloss of material due to cutting is reduced as compared to unit cellsbeing formed in the expanded configuration. One of skill in the art willappreciate other methods of making the stents and other medical devices.

Thick struts 12 and thin struts 14 define openings 18 having an area.The size of openings 18 varies in response to the relative position ofstruts 12 and 14. In particular, as stent 10 transitions between anexpanded configuration described in FIG. 1 to the collapsedconfiguration described in FIG. 2, the size of openings 18 decreases.Likewise, the outer diameter of stent 10, which is tubular with acircular cross-sectional profile, also decreases. Stent 10 may also betransitioned from the expanded configuration described in FIG. 1 to thecollapsed configuration described in FIG. 2 by the application of forcein a radially-inward direction. Such a transition is appropriate forcoupling stent 10 to a delivery device. For example, stent 10 may becoupled onto a stent delivery device such as a balloon catheter. Incertain embodiments, stent 10 is placed over a balloon catheter 500 andcrimped into place over the balloon.

When stent 10 is transitioned to the collapsed configuration describedin FIG. 2, thin struts 14 move from an expanded position to a collapsedposition closer to thick struts 12. Movement of the thin struts 14 maybe initiated by a radially inward force to stent 10. Thin struts 14 passa critical point after which time thin struts 14 “snap” to the stablecollapsed position closer to thick struts 12 without additional externalforce. Likewise, stent 10 may be transitioned to the expandedconfiguration described in FIG. 1. Movement of thin struts 14 may beinitiated by a radially outward force being applied to stent 10, such asa radial outward force from a balloon catheter. After application of anamount of sufficient force to reach a transition point at which force isreduced and the thin struts 14 “snap” to the expanded position withoutadditional application of outward force. Materials having desiredelasticities, such as the cobalt-chromium alloy, undergo this “snapping”into place and resist recoil when further expanded from the stableexpanded state or further compressed from the stable collapsed state.

As shown, stent 10 may be coupled to a balloon catheter 500. In certainembodiments, the stent 10 is delivered to the balloon catheter 500 in astable expanded configuration. Application of a compression force tostent 10 may result in the balloon catheter 500 collapsing through thetransition point where no further force is required for the stent 10 toassume the stable collapsed configuration. In certain embodiments, theballoon catheter 500 has a diameter greater than the diameter of thestent 10 in the stable collapsed configuration. In such embodiments, thestent 10 may grip the balloon catheter 500 because it exerts an elasticforce (in the inward direction toward the stable collapsedconfiguration) on the balloon catheter. In certain embodiments, asfurther discussed herein, stent 10 may be plastically deformed by acompressing force, such that the stent 10 assumes a smaller diameterthan in its stable collapsed configuration.

In certain embodiments, stent 10, or other medical devices having unitcells described herein, may be configured to have a plurality ofcollapsed and expanded configurations. For example, stent 10 may includetwo or more types of unit cells. In some embodiments, the two or moretypes of unit cells may require different amounts of forces fortransitioning the cell from the first stable position to the secondstable position. For example, a stent 10 may have a first unit cell typeand a second unit cell type. Each cell type may include a thick strutand a thin strut. However, the thin struts may have differentthicknesses and require different amounts of force to transition thethin strut from the collapsed position to the expanded position, or viceversa. In particular embodiments, the diameter of a multi-stable medicaldevice may be adjusted through a series of stepwise configurations.Accordingly, the device may be well suited for supporting a variety ofpassageways.

FIG. 3A shows the amount of crimping or collapsing force on the two unitcells shown in FIG. 3B. As shown in FIG. 3A, the enhanced line showscrimping force versus diameter (mm). The conventional plot represents aunit cell of a conventional balloon expandable stent. In the (a)configuration shown in FIG. 3B, the unit cells begin from a stableexpanded configuration. While the enhanced plot of FIG. 3A represents acrimp force being applied to the cells in the stable expandedconfiguration, it is also contemplated that a crimp force could also beapplied from a plastically deformed expanded configuration or a stablecollapsed configuration.

Upon application of a crimping force to the unit cells in the (a)configuration, one unit cell begins to collapse. When sufficient forcehas been applied to reach the inversion point (denoted as (b) in FIG.3A) of one of the unit cells, one unit cell has a reduced area as shownon configuration (b) of FIG. 3B. It is at this point that the thin strutof the unit cell moves to the collapsed position without application ofadditional force.

After collapsing unit cell through inversion point (b), the cellcontinues to close to the configuration shown in configuration (c) ofFIG. 3B upon application of the crimp force. The crimp force isdecreased as the strut transitions from configuration (b) toconfiguration (c). At point (c) in FIG. 3A, the first unit cell haspassed through the inversion point and has reached a stable collapsedconfiguration as shown in configuration (c) of FIG. 3B.

The second unit cell may also pass through an inversion point uponapplication of a crimping force. Point (d) of FIG. 3A shows the amountof force required to reach the inversion point of the second unit cell.At this point, the two unit cell embodiments adopt configuration (d) ofFIG. 3B, which represents the geometry at which the cell may transitionto the collapsed position without application of additional force.

As the second unit cell passes through the transition point, it snapsclosed to configuration (e). This configuration is represented as point(e) in FIG. 3A. In this configuration, the unit cell may elasticallyoppose an amount of force that is less than the force required totransition the cell back to the stable expanded configuration or theamount of force required to plastically deform the cell to a plasticallydeformed collapsed configuration.

It should be noted that the force required to collapse a supportstructure that has a plurality of rows of different types of cells maybehave in a similar manner. It also should be note that the diameter andapplication of force may vary depending on the exact construction of theunit cells of the medical device. The conventional designation of FIG.3A shows the amount of force required to crimp a conventional balloonexpandable stent. Since the unit cells of such stents do not havestructures and geometries like those described herein, the unit cells donot pass through the same types of inversion points (points ofdecreasing force).

Referring to FIG. 3C, the designated enhanced plot shows the appliedforce versus diameter curves for a stent comprising two unit cell typesas shown in FIG. 3B. The device having the two cells types in the stableexpanded configuration has an initial diameter of about 1.8 mm. Thedevice may then be crimped. This external force to the device isrepresented as a negative force in the graph. As demonstrated in FIG. 3Aand discussed above, the first unit cell type passes through a firstinversion point where the applied external force is reduced. The firstcell then passes through to a stable collapsed state, wherein the stenthas a first diameter of about 1.3 mm. The second unit cell may passthrough a second inversion point where the applied external force isreduced. The second unit cell then passes through to a stable collapsedstate, such that the stent has a smaller diameter of about 1.1 mm. Thistype of behavior may be seen with stents having two cell types whichrequire different amounts of forces to collapse the various cell types.In certain embodiments, this type of behavior may be observed whendifferent portions of a stent are collapsed.

As can further be seen in FIG. 3C, additional external force is appliedto crimp the enhanced stent. Such external force plastically deforms thestent to a reduced diameter. Upon ceasing the external force, the stentcomprising the two unit cells type recoils. Notably, such recoil is lessthan the conventional balloon expandable stent shown in the conventionalplot in FIG. 3C. As can be seen in the conventional plot, a conventionalballoon expandable stent may be crimped from a starting diameter of 1.8mm to the same minimum diameter as the enhanced stent. However, uponceasing the force to the conventional balloon expandable stent, thestent recoils to a diameter greater than that of the enhanced stent.

Application of outward radial force to the enhanced stent in the crimpedconfiguration results in elastic expansion of the stent. Such force maybe delivered to the stent by a balloon. As shown in the graph, the stentundergoes elastic and plastic expansion as this outward radial force isapplied. At about 0.3 units of force, the enhanced stent reaches aninversion point where one or more cell types of the stent pass throughthe inversion point. Thus, the amount of applied radial force decreases.Such decrease in radial force may be seen as a small valley between 1.2and 1.3 mm. As the enhanced stent is expanded through this stableexpanded configuration, applied force is continually in an elastic andplastic regime through the stable expanded configuration. In comparison,the conventional plastically deformable stent experience no such releaseof energy as it does not have inversion point geometry. Thus, no valleyis seen for the conventional stent.

The enhanced stent is then further expanded into a plastic regime.Application of a force capable of deforming the stent increases thestent diameter to about 2.8 mm. Upon removal of the force, the stentrecoils to a diameter of about 2.75 mm. As compared to the conventionalstent, the enhanced stent demonstrates reduced recoil, resulting in alarger diameter plastically deformed expanded configuration.

FIGS. 4-6A depict a section of a supportive structure that is displayedin a flattened profile. This section 22 of device 20 may be obtained bysevering a row of connector members 24 and unrolling section 22 from atubular shape into a flat shape. While certain embodiments are describedherein in terms of a flattened profile of a tubular structure, it isunderstood that flattened profiles may also be shown of devices nothaving a tubular structure. Thick strut 26 is connected to thin strut 28by connector members 24. Openings 30 are defined by thick strut 26 andthin strut 28.

FIG. 4 depicts section 22 with thick strut 26 and thin strut 28 in afirst predetermined stable expanded configuration. In some embodiments,this configuration may be appropriate for positioning device 20 over adelivery device prior to crimping, as further described herein. Whiledevice 20 has a predetermined expanded diameter, the diameter of device20 may be further expanded upon plastic deformation of the unit cells.

FIG. 5 depicts section 22 having a first predetermined stable collapsedconfiguration. In this configuration, thin strut 28 has beentransitioned to a stable position toward the corresponding thick strut26 of the unit cell opening 30. This collapsed configuration may beobtained by applying a radial inward force to device 20 in an expandedconfiguration. For example, device 20 having an expanded configurationas shown in FIG. 4 may be transitioned to the collapsed configuration byapplying a compressive force, e.g., crimping. Likewise, device 20 may beexpanded from the collapsed configuration as shown in FIG. 5 to theexpanded configuration as shown in FIG. 6A by the application of aradial outward force to device 20.

Advantageously, certain embodiments of devices, such as the device shownin FIGS. 5 and 6, may include plastically deformable unit cells. Assuch, one or more unit cells of device 20 may be capable of assuming aplurality of plastically deformed configurations, whether theseconfigurations are plastically deformed collapsed configurations orplastically deformed expanded configurations.

In some embodiments, it may be desirable to plastically deform device 20to an expanded configuration wherein the device has a greater diameterthan the expanded configuration shown in FIG. 4. FIG. 6A describes unitcells of section 22 of device 20 after plastic deformation has occurred.In this embodiment, thin struts 28 have been plastically deformed awayfrom thick struts 26. Plastic deformation may reduce the recoil that mayotherwise occur when a material is elastically displaced. Moreover,plastic deformation of the cells may alter their characteristics, sothat the cells no longer tend to “snap” back to a predetermined stableexpanded configuration.

In certain embodiments, device 20 may be configured to obtain aplastically deformed diameter selected from a continual range ofdiameters larger than the diameter of the predetermined stable expandedconfiguration. The one or more unit cells of device 20 may be expandedfrom the predetermined stable expanded configuration to a plasticallydeformed expanded configuration. To accomplish this, an outward radialforce may be applied to device 20. Such force may be greater than thetotal elastic strain limit of the portion of the unit cells beingplastically deformed. Once the elastic strain limit is reached, theplastically deformed unit cell may continue to be expanded and deformedin response to a radially-outward force resulting in a larger diameterof device 20. This diameter may be increased to any plastically deformeddiameter along a continuum as desired within the range of structuralintegrity of device 20. Such plastic deformation can occur withoutlimitation to a select number of step-wise diameters.

In certain embodiments, device 20 may be configured to obtain aplastically deformed diameter selected from a continual range ofdiameter less than the diameter of the predetermined stable collapsedconfiguration. With reference to FIG. 6B, device 20 is shown in aplastically deformed collapsed configuration. To achieve suchplastically deformed collapsed configuration, an inward radial force maybe applied device 20 in the predetermined stable collapsedconfiguration, as shown in FIG. 4. Such inward force should be greaterthan the elastic strain limit of the portion of the unit cell beingplastically deformed. Once the elastic strain limit is reached, theplastically deformed unit cell may continue to be collapsed and deformedin response to radial inward force resulting in a smaller diameter ofdevice 20.

FIGS. 7-9 demonstrate other flat profiles of supportive structures inaccordance with certain embodiments. FIG. 7 depicts supportive structure40 having five columns 42 of cells (columns may also be referred to asrings). Thick struts 44 and thin struts 46 define openings 48 and areconnected by articulations 50.

In some embodiments, articulations 50 are configured to provide spacingbetween thick struts 44 and thin struts 46. In certain embodiments, suchspacing provides certain advantageous properties to the unit cell. Insome embodiments, the spacing is configured to provide flexibility tothe cell when in a collapsed or an expanded configuration. As such, thespacing may be configured such that one or more unit cells adapt tocurvatures, relief, or other particular architecture of the lumenpassageway when collapsed or expanded. In certain embodiments, thearticulations may be configured to geometrically change the amount offorce required to reach the inversion point of the cell.

Adjacent columns 42 of unit cells may be connected by rowinterconnectors 52. Interconnectors 52 allow adjacent columns 42 to bedisplaced relative to one another. Interconnectors 52 are S-shaped bentconnect bars having at least one peak and one trough. In certainembodiments, interconnectors 52 may have two or more bends.Interconnectors 52 connect adjacent cells which are substantiallylateral to each other. Interconnector 52 may be spaced apart by adistance from other interconnects in same axis by one or more unitcells. As shown, interconnectors 52 are spaced apart by two unit cells.In certain embodiments, interconnectors 52 have substantially the samethickness as the thick strut 44 or the thin strut 46. In certainembodiments, interconnectors 52 have a thickness less than thick strut44 or thin strut 46. In certain embodiment, thickness or pliability ofinterconnector 52 may be varied such that the supportive structure 40 isadapted to conform to the deployment lumen. In certain embodiments,interconnectors 52 are configured for better nesting of the supportivestructure 40 in a collapsed or crimped configuration.

In certain embodiments, articulations 50 and interconnectors 52 providesupportive structure 40 with the ability to adapt to certain lumenarchitectures. In some embodiments, the combination of the articulations50 and interconnectors 52 provide spacing between unit cells such thatone or more unit cells of device 40 may be displaced relative to itsmanufactured, crimped, or deployed position. Off-axis displacement of aunit cell relative to the longitudinal axis of the tubular supportivestructure 40 unit cell may be obtained within ranges of flexibility ofthe articulations 50 and interconnectors 52.

FIG. 8 depicts supportive structure 60 having six columns 62 of cells.Thick struts 64 and thin struts 66 define openings 68 and are connectedby articulations 70. Column interconnectors 72 connect adjacent columns62, and allow adjacent columns 62 to be displaced relative to oneanother. As shown, an interconnector 72 extends between an articulation52 of one cell to an articulation of another cell in an adjacent column62. Interconnector 72 extends along thin strut 62 and bends to adirection substantially parallel to the axis of a column 62 of cells.Interconnector 72 extends in the substantially parallel directionbetween adjacent columns 62 in the axis of the columns 62.Interconnector 72 bends to extend along the thick strut and joinsarticulation 70 of a cell in an adjacent row. As shown, interconnectorjoins laterally displaced unit cells. In certain embodiments, thedisplacement between interconnected unit cells may be varied dependingon the application.

FIG. 9 depicts supportive structure 80 having six columns 82 of cells.Thick struts 84 and thin struts 86 define openings 88 and are connectedby articulations 90. In some embodiments, articulations 90 have a lengthwhich is approximately equal to half the distance between the apices ofthin strut 86 and thick struts 84 of the same unit cell. In someembodiments, the length (in the axis of the columns) of the articulationcan be about 5 to about 50 percent of the distance between the apices ofthe thin and thick struts of the same unit cell. In certain embodiments,articulations 90 may have varying lengths. In the embodiment shown,adjacent column interconnectors 92 extend between articulations 90. Insuch articulations, the distance may be increased to accommodate thethickness of interconnectors 92. Interconnectors 92 extend fromarticulation 90 of a unit cell in a column 82 of unit cells to anarticulation 90 in an adjacent row. In this embodiment, interconnector92 has a similar shape to the interconnectors shown in FIG. 8. However,interconnector 72 joins adjacent cells which displaced to a lesserdegree than that shown in FIG. 8.

In certain embodiments, unit cells may be configured such that the thickstruts and thin struts are arranged in a repeating pattern that isconsistent throughout the supportive structure. In certain embodiments,the pattern may vary within the same column or different columns of unitcells. For example, two adjacent unit cells within the same column maybe arranged such that the thick struts of each cell are adjacent and areconnected through joints or articulations. Such a pattern may repeatsuch that the thin struts are also adjacent to other thin struts and areconnected to each other by articulations. In certain embodiments, such apattern may repeat throughout the structural support or within certaincolumns. In one embodiment, adjacent columns may oppositely arrangedunit cells (e.g., thick struts on top in the first column and thickstruts on bottom in the second, adjacent column, relative to a planararrangement).

While FIGS. 7-10 show certain types of cells structures, cellinterconnectors, and articulations, many different types of these areknown in the art and may be used. In certain embodiments, other types ofcell structures using principles described herein may be used. Incertain embodiments, various types of cell interconnectors may be usedincluding, but not limited to valley to valley interconnectors, side toside interconnectors, valley to side interconnectors, peak to sideinterconnectors, or peak to peak connectors may be used in someembodiments. In certain embodiments, interconnectors may have variousthickness and configurations. In certain embodiments, spacing betweeninterconnectors may vary depending on the application. Moreover,described in FIGS. 7-10 are various features of structural supports. Itis intended that one or more of these features may be incorporated intoany embodiment described herein.

FIGS. 10A-10E depict two exemplar cells of the device 40 in a flattenedprofile. FIGS. 11A-11E depict a single column 42 of unit cells of device40 arranged in a tubular structure. In one embodiment, device 40 isformed such that openings 48 are spaced as described in FIGS. 10A and11A. As such, thick struts 44 are separated from thin struts 46 anddevice 40 may be configured to have a predetermined stable collapsedconfiguration and an expanded configuration. As shown in FIGS. 10A &11A, the unit cells are shown in the expanded configuration.

Device 40 or a similar device may be coupled to a suitable deliverydevice. For example, if the delivery device is a balloon catheter,device 40 may be placed around the balloon catheter in the vicinity ofthe balloon. Device 40 may then be transitioned toward the collapsedstate by crimping or otherwise applying a radially-inward directedforce. In some applications, it may be desirable to collapse device 40to the fully collapsed position. In other applications it may bedesirable to prevent the contraction of device 40 to the fully collapsedstate by interaction with the delivery device. In such embodiments, theouter diameter of the delivery device may be greater than the diameterof the device in the stable collapsed configuration, but smaller than adiameter where the force is reduced during compression or contraction ofthe device, as discussed above. As such, the device 40 would apply aninward force on the delivery device, e.g., on the balloon catheter.

FIGS. 10B and 11B depict the respective portions of device 40 aftercrimping to a desired diameter. Such configuration is achieved byapplying a radially inward force to device 40 sufficient to transitionthe one or more cells of the device from the stable expandedconfiguration to the stable collapsed configuration and sufficient toplastically deform the unit cell to a plastically deformed collapsedconfiguration. However, recoil of stent may result in an increaseddiameter which is shown in FIGS. 10C and 11C. However, such recoil isless than that which may occur when crimping of other plasticallydeformable designs formed of similar materials.

Referring to FIGS. 10C and 11C, device 40 may be plastically deformed toa collapsed diameter less than the predetermined stable collapseddiameter. A radially inward force may be applied to the device 40 in thepredetermined stable collapsed configuration. Such force must besufficient to plastically deform the unit cell.

Referring to FIGS. 10D and 11D, device 40 is shown in an expandedconfiguration achieved by applying sufficient radial outward force toplastically deform the device from the predetermined stable expandedconfiguration. As the outward force is increased, device 40 may undergoexpansion and may then begin to plastically deform. As the difference inthe sizes between thick struts 44 and thin struts 46 is increased, asimilar difference may be seen in the amount of plastic deformationbetween those two components. While the device 40 in this configurationmay incur some recoil resulting in the plastically deformed expandedconfiguration shown in FIGS. 10E and 11E, the amount of recoil is lessthan that of conventional balloon expandable supporting structures orthose structures which use a nonpreferred material (e.g., highly elasticmaterial).

While there are various states of plastically deformed expansion, oneexample in the continuum of deformation is described in FIGS. 10E and11E. It will be appreciated that device 40 need not be deformed to thisdegree, or alternatively, may be deformed further to result in a stilllarger outer diameter. Because device 40 is expanded plastically, itsdiameter need not be limited to discrete predetermined dimensions.

FIGS. 12A and 12B show one embodiment of a unit cell 110 incorporatedinto a portion of a medical device. The portion of the medical deviceincludes a repeating pattern 115. The medical device incorporating theunit cell 110 can be a stent or other lumen support or other medicaldevice as discussed herein. Although the unit cell 110 is incorporatedinto a repeating pattern, it can be used in structures that do notrepeat in a regular manner. In this embodiment, the repeating pattern115 includes a plurality of unit cells 110 arranged in a plurality ofrows of and in a plurality of columns.

The orientation and position of the unit cells 110 can be varied fromrow to row, within a row, from column to column, or between columns. Inthe illustrated embodiment, the unit cells of adjacent rows are arrangedin opposite directions. In particular, a row 100 is arranged in a mannerso that a thick strut 102 of a first unit cell in the row 100 is on thetop and a thin strut 101 is on the bottom. In an adjacent row 105, thethick strut 102 of a second unit cell in the adjacent row 105 is on thebottom and a thin strut 101 is on the top. “Top” and “bottom” as used inthis paragraph is relative to the unit cells as shown in FIG. 12A. Thisalternating configuration of unit cells in adjacent rows assists innesting of the device when in its collapsed configuration in someembodiments.

The repeating pattern 115 also includes a plurality of interconnectors105 that interconnect different rows of the pattern. For example, in theillustrated embodiment, the interconnect 105 connects the adjacent rows100 and 105. As with other interconnects discussed herein, theinterconnect 105 can extend from a peak of a unit cell of oneembodiment.

The interconnector 105 can have any suitable geometry and configuration.For example, the interconnector 105 can have a first end 116 configuredto couple with a first row and a second end 117 configured to couplewith a second row. In some embodiments, the interconnector 105 has anelongate portion 118 between the first and second ends 116, 117 that isselected to enhance a performance characteristic of the pattern 115. Forexample, FIG. 12B illustrates that the elongate portion 118 is shaped sothat the first and second ends 116, 117 extend away from lateral side ofunit cell to which they are coupled, e.g., generally perpendicular to alongitudinal axis of the rows in which the unit cells are located and sothat the elongate portion extends generally parallel to the longitudinalaxis of the rows in which the unit cells are located. This arrangementprovides for a more compact geometry at least in an unexpanded state.

The length of the interconnect 105, e.g. of the elongate portion 118thereof, can be selected to enhance a performance characteristic of thepattern 115. For example, the interconnect 105 can be configured tocouple peaks of unit cells that are adjacent to each other in thecollapsed state. Alternatively, the interconnect 105 can be configuredto couple peaks of unit cells that separated by at least one interveningpeak in the adjacent row when the pattern 115 is in an unexpanded state.In the illustrated embodiment, each interconnect 105 connects peaks ofunit cells in adjacent rows that are separated by at least oneintervening unit cell in the collapsed state. FIG. 12A shows that thepattern 115 permits the adjacent rows to shift such that no interveningpeaks separate the peaks to which the interconnect 105 is connected.

In some embodiments, interconnect 105 has a sinusoidal geometry.However, the interconnect 105 may also have other geometries describedherein. In one embodiment, the interconnect 105 is spaced apart fromadjacent interconnects such that the interconnects do not contact eachother when in the collapsed configuration, shown in FIG. 12B.

As discussed above, each unit cell also preferably is coupled to anadjacent unit cell along each row by an articulation 107. As discussedin more detail herein, articulations 107 enhance the plasticdeformability of the unit cells, e.g., from a stable collapsed state toa crimped state, wherein the device or structure has a reduced diameter.In some embodiments, the articulations 107 mechanically isolate adjacentunit cells so that the adjacent unit cells are less rigid and are ableto be plastically deformed to a greater extent than if the unit cellswere directly coupled together. The articulations 107 can also enablethe unit cells to plastically deform under a lesser force or pressure tothe same extent than would be needed to expand unit cells that weredirectly coupled together.

The articulations 107 can take any suitable configuration. For example,in one embodiment, the articulation 107 includes a first end 120 that iscoupled with a first unit cell 125 and a second end 121 that is coupledwith a second unit cell 130. The connection between the articulation 107and the unit cells 125, 130 can be at any suitable location, forexample, at adjacent valleys of the two cells. In one arrangement, thearticulation connects a thin strut of one unit cell with a thick strutof an adjacent unit cell. In some embodiments, the articulation 107 hasa length between the ends 120, 121 that can be varied based upon adesired characteristic. For example, it may be desirable to elongate thearticulation 107 to provide greater mechanical isolation betweenadjacent cells. On the other hand shortening the articulation 107 wouldprovide a more compact arrangement. The articulation 107 is at least atlong as the thickness of the thin strut 101 in one embodiment. Inanother embodiment, the articulation 50 is at least at long as thethickness of the thick strut 102.

FIG. 13 shows a unit cell 150 undergoing a crimping process.

In FIG. 13(a), the unit cell 150 is in a stable expanded configuration.The unit cell 150 is similar to those hereinbefore described and thedescriptions of those cells are applicable to the unit cell 150. Inparticular, the unit cell 150 has a thin strut 151 and a thick strut152. The thick and thin struts 152, 151 can be configured as elongatedmembers extending between first and second ends 160, 161. The first ends160 can be coupled together and the second ends at apices 165, 166. Theapices 165, 166 are described elsewhere herein as “peaks” of the unitcell 150.

The apices 165, 166 can take any suitable form. In one embodiment, theapices 165, 166 have a portion which has localized thinning. In certainembodiments, such thinning is configured to promote flexibility of thethin strut from a collapsed position to an expanded position. As such,the apices may be used to control force required to reach the inversionpoint between the thick strut 152 and thin strut 151. In certainembodiments, the elongate member 175 of thick strut 152 may have varyingthickness near apices 165. In certain embodiment, the elongate member175 of thick strut 152 has a thickness that ranges between about 150 toabout 200 percent compared to that of the apex 166 of the thin strut151.

In some embodiments, the unit cell 150 is configured to couple to otherunit cells, for example to form a repeating pattern suitable for formingall or a portion of a stent or other lumen supporting medical device. Inone embodiment, an articulation 170 is located along the length of theelongate member 175 of the thick strut 152. In one embodiment, anarticulation 170 is located along the length of the elongate member 178of the thin strut 151. In one embodiment, the unit cell is configuredsuch that at least in one expanded configuration the elongate member175, 178 of at least one of the thick strut 152 and the thin strut 151have a concave shape. In one arrangement, both of the thin strut 151 andthe thick strut 152 have a concave shape such that the unit cell 150 hasa diamond shape in at least one expanded configuration, as shown in FIG.13(a).

FIG. 13(b) illustrates that application of an inward force (e.g., aradially inwardly applied force) on the unit cell 150 causing the thinstrut 151 to move toward the thick strut 152. F₁ represents an amount offorce that unit cell 150 elastically opposes. Such amount of force maybe applied, however, cessation of the force would result in the cellexpanding to the expanded position shown in FIG. 13(a). This causes thedistance between the thick strut 152 and the thin strut 151 to bedecreased at least at a location spaced from the apices 166, 165, andcauses the unit cell to be compressed through the inversion point to apredetermined stable collapsed configuration 125.

FIG. 13(c) further illustrates an inversion point configuration 126 ofunit cell 150. The designation e shows the elastic regime from theinversion point to the predetermined stable collapsed configuration.Each unit cell 150 is configured to have an inversion configuration 126.Such configuration 126 is a configuration in which the unit cell maymove between stable collapsed and expanded configurations without theapplication of addition force. The inversion point configuration 126 isa configuration at which a force suddenly decreases to complete thetransition to the collapsed or expanded configuration. In certainembodiments, described herein the inversion point geometry is used tominimize recoil in materials that would otherwise recoil beyond anacceptable range. F₂ represents a sufficient amount of force totransition the unit cell 150 from the stable expanded position shown inFIG. 13(a) to the inversion point at which no additional force isrequired to complete the transition from the expanded position to acollapsed position. Thus, F₂ is greater than F₁.

FIG. 13(d) shows that further application of an inward force to unitcell 150. Such inward force plastically deforms the stent. F₃ representsa plastically deformable amount of force. Such amount of force mustexceed the elastic strain limit of the thin strut. In certainembodiments, F₃ is be greater than the force used to reach the inversionpoint F₂, but this depends on the exact configuration of the strutsegments. In certain embodiments, articulation 170 may be configurationto have a shape which allows plastic deformation of the unit cell 150 toconfiguration 131

FIG. 13(e) illustrates the effect of recoil on the collapsed state ofthe unit cell 150. Once a sufficient amount of crimping force, F₄, hasbeen applied to unit cell 150, the thin strut 151 elastically recoils.Thus, designation f represents this amount of elastic recoil, which canbe measured as a distance. Thus, the unit cell transitions from thefully deformed state 131 to the free state 135 in which it has aplastically deformed collapsed configuration.

Referring to FIG. 14A, a schematic drawing represents a conventionalballoon expandable stent without desired geometries which allow thestent to pass through an inversion point. As such, the conventionalballoon expandable stents has a high degree of recoil. Such stents areplastically deformable through a series of configurations (1a), (2a) andto the collapsed diameter (4a). However, such stents demonstrate a highdegree of recoil denoted as a.

Referring to FIG. 14B, a balloon expandable stent having the geometriesdiscussed herein and made of certain elastic materials may pass througha series of expanded configurations (1b) and (2b) and through aninversion point to reach configuration (3b) (also designated as thepredetermined stable collapsed configuration). Upon application of aplastically deformable crimp force and then release, the stent exhibitsreduced recoil when compared to the regular balloon expandable stent ofFIG. 15.

FIG. 15 shows a comparison of a conventional balloon expandable stentsmade of certain materials compared to stents having bistable geometriesthat have an inversion point and which are capable of undergoing plasticdeformation. As discussed above, the material and the geometry of thestent contributes to reduced recoil when compared to other stents madeof different materials or having different geometries. Stents made ofmaterials having different elastic ranges are shown.

Referring to FIG. 15(a), stainless steel conventional balloon expandablestents expand by means of elastic and plastic deformation (E+P) fromcollapsed diameter (1) to desired expanded diameter (4). However, thisis followed by elastic recoil (−E) to a diameter (6) within anacceptable range (5) that will provide good clinical outcomes. Inparticular embodiments, described herein, this acceptable range (5) isabout 10% of the expanded diameter of the stent. As shown, thisstainless steel type stents recoil within an accepted range, which hasled to the common use of this type of stent.

Referring to FIG. 15(b), a convention Cobalt-x-y alloy stent is shown,such as stent made of L605 or MP35N. The elastic recoil (−E) fromexpanded diameter (4) is greater, approximately twice that of stainlesssteel shown in FIG. 15(a). Such recoil is outside of the accepted rangeof recoil, leading to a smaller stable diameter (6) that could lead toless desirable clinical outcomes. This can only be overcome by expandingthis stent beyond expanded diameter (4), so that a clinically acceptablerecoil diameter is achieved. However, that type of expansion requireshigher pressures in the case of balloon expansion during angioplasty,and greater diameter expansion. Such conditions may damage tissue at theedges of the stent.

FIG. 15(c) shows one embodiment of the invention described herein. Sucha stent may be made with materials such as a cobalt alloy, such as L605or MP35N. During expansion, the stent passes from predetermined stablecollapsed configuration (2) to predetermined expanded configuration (3)through an inversion point in which elasticity is reversed and releasedby the stent. Thus, less elastic recoil potential is built up duringfurther deformation from predetermined stable expanded configuration (3)to plastically deformed expanded configuration (4). Hence, the stentrecoils to diameter (6). As shown, the recoil is less than thatexperienced by example (a) or (b). Less elastic recoil provides a widerlumen passageway, which is known to provide better clinical outcomes.Such geometry overcomes one of the disadvantages generally associatedwith higher elastic alloys, namely elastic recoil outside of anacceptable range.

Referring to FIG. 15(c), an elastic range exceeding preferred valuesresults in recoil beyond an acceptable range of recoil, even when thestent geometry allows the stent to pass through the inversion pointbetween a predetermined stable collapsed configuration (2) and apredetermined stable expanded configuration (3).

FIG. 15(e) illustrates a highly elastic stent, such as one that usesNitinol or other materials with greater than 1% and up to about 8% orhigher elastic range. As diagramed here, such stents expand only byelastic energy from (2) to (3), with (3) being the final dimension andcan be achieved to similar diameters as shown by position (4). However,such stents lack beneficial radial strength and radiopacity properties.

Referring to FIG. 16, two unit cells 200, 201 of a device are shown.Such unit cells are demonstrative of certain inventive features ofpreferred unit cells having thick strut 207 and thin strut 206. Thesefeatures may also be seen in and are applicable to other figuressubmitted herewith. One or more of the various features of these unitcells 200, 201 may be used together with one or more other features ofunits cells described herein (e.g., interconnectors, various widthstruts).

In this embodiment, thick strut 207 and thin strut 206 are connected atthe corners of the unit cell by hinges 210. Hinges 210 are shown as partof the thick strut 207 and thin strut 206. The hinges can take anysuitable form, so long as they permit or enhance movement of one moreboth of the struts 207, 206 about the hinge. In one embodiment, to formhinges 210, the thickness of thick strut 207 is tapered to a thicknessapproximately equal to the thickness of thin strut 206. In someembodiments, hinge 210 may be formed by a gradual taper of thick strut207 to a reduced thickness greater than the average thickness of thinstrut 206. In certain embodiments, hinge 210 may also be formed by athin portion of thin strut 206. For example, the hinge portion 210 ofthin strut 206 may have a reduced thickness as compared to the averagethickness of thin strut 206. As shown, the thickness of thin strut 206is approximately equal to the thickness of hinge portion 210.

Further referring to FIG. 16, thick strut 206 may comprise a baseportion 211. Base portion 211 comprises several notable features. Inthis embodiment, base portion 211 comprises two convex portions 230, andconcave portion 220. In certain embodiments, the base portion isconfigured to allow substantial resistance to plastic deformation of thethick strut 207. In some embodiments, base portion 211 also includesarticulation 215. Articulation 215 is geometrically configured to allowplastic deformation of the individual cells. Articulation 215 createsspacing between thin strut 206 of unit cell 200 and thick strut 207 ofunit cell 201. Such spacing provides an area between the thin and thickstruts, such that the unit cells may be plastically deformed beyond thepredetermined stable collapsed configurations.

Referring to FIG. 17, a stent 240 having a collapsed configuration isshown. Between thin strut 206 and thick strut 207, an articulation 215is present which allows plastic deformation of stent 240 to a crimpedconfiguration. As shown, stent 240 may be coupled to balloon catheter501. In certain embodiments, a balloon catheter 501 may be deliveredover a guidewire to the body lumen where the stent is to be deployed.

Referring to FIGS. 18A and 18B, one embodiment of a device includes oneor more open unit cells. Such devices may include only open cells or acombination of open and closed cells. In certain embodiments, such openunit cells may have a predetermined stable expanded configuration (shownin FIG. 18A) and predetermined stable collapsed configurations. Incertain embodiments, such unit cells may also be plastically deformed tocollapsed or expanded configurations. In certain embodiments, thevarious arms of the thin and thick struts may have different stiffnessor thicknesses as desired. Designs of open unit cells may be taken tomore complicated patterns having various strut undulations and hingepoints. Such variables may provide various inversion points which allowcertain sections of the open cell to pass through various collapsed orexpanded configurations.

Embodiments also include methods of using a medical device having one ormore plastically deformable multistable cells. As discussed above, stent40 may be loaded onto a stent delivery catheter. In some embodiments,the stent is crimped or collapsed onto a stent delivery catheter. Incertain embodiments, the stent is collapsed to the predetermined stablecollapsed configuration thus decreasing the diameter of the stent.

In certain embodiments, the stent delivery catheter may have a diametergreater than the diameter of the predetermined stable collapsedconfiguration. If the inner diameter of the collapsed stent is slightlysmaller than the outer diameter of the balloon catheter, then the stentwould tend to apply radially-inward force on the catheter. Thisphenomenon may occur as the cells, which have passed the transitionpoint, act under internal forces to attain the predetermined stableconfiguration. As a result, the stent may “squeeze” the catheter withoutthe need for the further application of an external force.

In some embodiments, the device having one or more unit cells may becrimped further, resulting in some degree of plastic deformation beyondthe collapsed configuration. In certain embodiments, a stent may beplastically deformed to a collapsed configuration having a smallerdiameter than the predetermined stable collapsed configuration.Advantageously, such stent designs allow for a smaller deploymentdiameter of the stent. Moreover, the stent may substantially maintainits smaller diameter stent profile upon plastic deformation, as thestent exhibits reduced recoil when compared to stents of differentdesigns.

Once coupled to the delivery device, a user may optionally place asheath or other external barrier around device 40. It will beappreciated that in some embodiments of the present invention, such asheath is not desirable, as it may unnecessarily increase the deliveryprofile.

Once positioned on the delivery device, the medical device may then beinserted into a body lumen. The medical device may be delivered to adesired deployment location within a blood vessel or other passageway.Once in the desired location, the medical device may be deployed.

Deployment of the medical device may occur in various fashions dependingon the medical device and the delivery device. In certain embodiments,the delivery device provides a radial outward force on the medicaldevice. Such force is sufficient to transition one or more unit cells toa stable expanded configuration. In certain embodiments, the stableexpanded configuration is the predetermined stable expandedconfiguration.

In some embodiments, the delivery device may disengage the medicaldevice once expanded to the predetermined stable expanded configuration.A user optionally may adjust the position of device 40 in the passagewaywhile in a predetermined stable collapsed or expanded configuration,depending on the size of the passageway.

In certain embodiments, a multistable medical device having two or morestable expanded configurations, which are not plastically deformedexpanded configurations, may be used. The medical device may be deployedin any of the stable expanded configurations. In some embodiments, themedical device having one or more cells may be expanded in a manner thatresults in a varied diameter along its length. For example, the balloonmay be deflated and repositioned, or another balloon may be expanded ata location within device 40, such that a force is applied to only aportion of device. As such, an area of device 40 may be expanded to alarger diameter than another area of device 40

In certain embodiments, the delivery device may be used to apply a forcesufficient to plastically deform the medical device from a predeterminedstable expanded configuration to a plastically deformed stable expandedconfiguration. In certain embodiments, the delivery device applies aforce to the medical device through mechanical means. In someembodiments, a balloon may be inflated to apply a radially-outward forceon device 40 and expand the diameter of device 40. In certainembodiments, the stent may be plastically deformed such that the stentcontacts and/or supports the passageway.

Once the device has been plastically deformed and expanded into adesired configuration, the catheter may be removed from the patient,leaving device 40 to support the passageway. Placement of device 40 maybe ascertained at this time, or earlier, by radiography or other knownmethods.

The stents and other medical devices described herein may be usedtogether with other known options and methods. For example, drugsoptionally may be combined with a stent having the design describedherein by coating the stent or using other known methods. One of skillin the art will appreciate that stents and other medical devices mayalso comprise a coating, such as a coating of one or more drugs,medications, or polymers. In particular embodiments, the medical device(e.g., stent) including the unit cells may be coated with a crosslinkedcollagen protein coating. Such stent would possess the clinical benefitsof being less thrombogenic and provide a medium for endothelium cellmigration across the device. In certain embodiments, a tie layer may beused to tie the coating to the unit cells.

As an example of the results obtainable by the present invention, thefollowing information is provided based in experiments that have beenconducted. A coronary stent constructed in accordance with the presentinvention was formed having an outer diameter of 1.8 mm when in theexpanded predetermined stable configuration. This stent was crimped to acollapsed configuration having an outer diameter of 0.8 mm. Then, thestent was expanded to a point in which plastic deformation occurred. Thefinal diameter of the stent was measured to be 3.0 mm. Thus, one ofskill in the art will appreciate the relationship between the compactdelivery profile and the attainable expanded diameter of this stent.

The various methods and techniques described above provide a number ofways to carry out the invention. Of course, it is to be understood thatnot necessarily all objectives or advantages described may be achievedin accordance with any particular embodiment described herein.

Furthermore, the skilled artisan will recognize the interchangeabilityof various features from different embodiments. Similarly, the variousfeatures and steps discussed above, as well as other known equivalentsfor each such feature or step, can be mixed and matched by one ofordinary skill in this art to perform methods in accordance withprinciples described herein.

Although the invention has been disclosed in the context of certainembodiments and examples, it will be understood by those skilled in theart that the invention extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses and obviousmodifications and equivalents thereof. Accordingly, the invention is notintended to be limited by the specific disclosures of preferredembodiments herein.

1-9. (canceled)
 10. A method of crimping a lumen support on a deliverydevice comprising: delivering a lumen support onto a delivery device,the lumen support comprising one or more unit cells, the one or moreunit cells having a thick strut and a thin strut and capable of assumingan original collapsed configuration or a plastically deformed collapsedconfiguration and an original expanded configuration or a plasticallydeformed expanded configuration, wherein no stable configurations existbetween the original collapsed configurations or the original expandedconfiguration; applying a radially inward force to the lumen support;and deforming one or more unit cells of the lumen support to aplastically deformed collapsed configuration.
 11. The method of claim10, further comprising transitioning the lumen support to a stablecollapsed configuration from a stable expanded configuration byapplication of a force through an inversion point of decreased force.12. The method of claim 10, wherein lumen support has a smaller diameterin the plastically deformed collapsed configuration.
 13. The method ofclaim 10, wherein the thin strut is more pliable than the thick strut.14. The method of claim 10, wherein the lumen support comprises amaterial having an elastic range between about 0.15 to about 1% and anelongation of about 30% and an ultimate tensile strength greater than500 MPa.
 15. (canceled)
 16. The method of claim 10, wherein the supportcomprises first flexible articulations and an interconnector configuredto allow one or more unit cells of a first column to conform to a lumen.17. (canceled)
 18. The method of claim 14, wherein the material is acobalt alloy.
 19. A balloon catheter comprising: a balloon; and a lumensupport device in a crimped configuration coupled to the balloon, thedevice comprising one or more unit cells capable of transitioning from astable collapsed configuration to a stable expanded configuration byapplication of a force through an inversion point of decreased force,the one or more unit cells capable of plastically deforming to anexpanded plastically deformed configuration; wherein the lumen supportdevice comprises a material having an elastic range between about 0.15to about 1% and an elongation of about 30% and an ultimate tensilestrength greater than 500 MPa.
 20. The catheter of claim 19, wherein thematerial is a cobalt alloy.
 21. The method of claim 10, wherein the thinstrut substantially conforms to the shape of the thick struck in theoriginal collapsed configuration.
 22. The method of claim 10, whereinthe plastically deformed collapsed configuration reduces the area of theunit cell.
 23. The method of claim 10, wherein the step of deforming theone or more or more unit cells decreases a distance from the thin strutto the thick strut.
 24. The method of claim 10, wherein the lumensupport comprises a medical device selected from the group consisting ofa stent, an occlusion device, a multistable valve, an expander, a clip,a loop, and a ring.
 25. The method of claim 16, wherein the firstflexible articulations are configured to geometrically change an amountof force required to reach an inversion point of the unit cell.
 26. Themethod of claim 16, wherein the interconnector displaces adjacentcolumns relative to one another.
 27. The method of claim 16, wherein theinterconnector is configured for better nesting of one or more unitcells in the original collapsed configuration or plastically deformedcollapsed configuration.
 28. The method of claim 16, wherein theinterconnect extends along the thin strut and bends in a directionsubstantially parallel to an axis of a column of unit cells in the lumensupport.
 29. The method of claim 16, wherein the interconnect extendsalong the thick strut and joins the first flexible articulation of aunit cells in an adjacent row of the lumen support.
 30. The ballooncatheter of claim 19, wherein an outer diameter of the balloon isgreater than a diameter of the lumen support in the stable collapsedconfiguration.